A hard disk drive stores digitally encoded data on circular plates, called platters. The platters are mounted on a spindle and rotate in unison at high speeds past read-write heads. The heads fly on sliders in close proximity to magnetic layers on the platters. Sensors write (record) and read (retrieve) the digitized data which is stored on the magnetic layers. The magnetic layers are protected with a thin carbon overcoat.
Disk drives are mounted in sealed housings to protect them against dust, humidity, and other contaminants. The flying heads are supported on cushions of air only nanometers (flying height) above the platters. The platters must be free of contaminants and imperfections to maintain an extremely close spacing (flying height) between the heads and platters. Modern hard drives have flying head heights of about 5 to 15 nanometers.
Head impacts [crashes] with platters, caused by power losses or low pressure at altitudes normally above 10,000 ft., can be catastrophic because important records can be permanently lost. Consequently, time consuming back-up records are frequently made to protect data, thus increasing the cost of doing business. Making back-up records is an inefficient use of valuable technical personnel. Crashes also result in expensive drive replacements.
Pressure, temperature and humidity affect the operation of a hard disk drive. If air pressure in a drive is too high, data will be improperly written and read. Air pressure is affected by temperature. Operating conditions in current drives are so critical that temperature compensation is provided to accommodate changes in the environment. Humidity over extended periods accelerates component corrosion. Corrosion of the magnetic layer is adversely affected if the carbon overcoat is not dense or thick enough to provide full coverage. When heads are parked for long periods of time, stiction can lead to hard drive failure and lost data. Stiction can occur especially if a hard drive has been out of use for an extended period. When the drive is powered up, the flying head can stick to the disk lubricant layer, potentially preventing the disk from rotating.
Wear, corrosion, manufacturing defects and head crashes are the major causes of hard drive failures. When crashes occur, heads scrape and damage platters. The current strategy is to prevent head contact on the data portions of platters. Impacts and contacts can occur during power down and power failures. Hard disk drive manufacturers have taken several actions to address these problems and thus extend drive life.
One action is to incorporate data free landing zones (“LZ”) usually near inner diameters of platters that heads contact during power down. The landing zones prevent head contact with data storage areas during start up and power down. Landing zones reduce storage space, increase cost and make mechanical tolerance control more difficult.
In newer drives, springs and the inertia of the rotating platters park flying heads in landing zones during unexpected power losses. Other technologies that are used include laser zone texturing (“LZT”) and head unloading (“HUT”). In laser zone texturing, stiction and wear are reduced by incorporating in landing zones, an array of smooth laser generated nanometer-scale “bumps”. In head unloading, during parking, heads are lifted off platters onto plastic “ramps” near outer edges of the platters, thus reducing shock forces and eliminating stiction during start up and powering down. Both technologies increase the cost, complexity and difficulty of manufacturing hard drives.
Competitive market pressures and software requirements have forced hard disk manufacturers to pursue increased drive capacities and reduced seek times (data rates). Drive capacity, typically designated in gigabits per square inch, is dependent on the areal density of the disk. Reduced seek times require friction reduction and increased rotational speed. Rotational speed is closely related to the lubricant on platters and lubricant is one of the factors that limit rotational speed. Imperfections, such as drive motor spindle bearing, out of roundness and runout, have limited increases in areal density and reduction of seek times. Manufacturers have reduced seek times by incorporating fluid dynamic bearings. Inasmuch as fluid bearings have no metal-to-metal contact, they do not affect disk loading and can handle higher disk rotational speeds.
For areal densities and data rates to increase, incidental crashes of flying heads must be prevented. Platter surfaces must be very smooth and defect free. For increases in areal density, the carbon overcoat that protects the magnetic data recording layer must be thinner however, a thinner overcoat may expose the magnetic layer to corrosion because of pin holes. Areal density can be increased by reducing the spacing between the recording transducer, or read/write head, and the magnetic layer of the magnetic recording disk. The magnetic spacing is the effective distance between the magnetic recording head and the magnetic media layer on the disk. The magnetic spacing consists of the flying height of the head, recession of the head pole tip, thickness of the carbon (DLC) film on the head and the thickness of the carbon and lubricant overcoats on the disk surface.
Vijayen, U.S. Pat. No. 6,537,668 discloses a diamond like carbon material for magnetic recoding media containing an amorphous carbon comprising carbon in the range between about 72 and 92 atomic percent and hydrogen in the range between about 8 and 18 atomic percent.
FIG. 2, a schematic of a current hard disk drive, shows the relationship between a flying head and a platter for an areal density, also referred to as storage density, of approximately 100 Gb/in2. A disk drive housing 100 encloses the platters and flying heads. A flying head consists of a slider 101 and a magnetic element 102, with carbon overcoat 103, typically 3 to 5 nm thick. The flying height 104 is the physical distance that separates the flying head and surface of the platter. The flying height ranges from 5 nm to 15 nm to achieve approximately 100 Gb/in2.
The hard disk substrate 108 of the platter, which may be fabricated from any number of materials, has a magnetic recording layer 107 that is protected with a carbon overcoat 106. In current drives the carbon overcoat 106 ranges from about 3 nm to 5 nm. A perflouropolyether (PFPE) lubricant film 105 is deposited on the carbon overcoat 106. The combination of the lubricant 105 and carbon overcoat 106 protects the magnetic data recording layer 107 from corrosion and mechanical damage from incidental contact with the recording head.